Telemetry

ABSTRACT

A remote telemetry metering system, includes one or more battery-powered metering units and a central data collection unit, each including a radio transceiver. The central data collection unit transmits a signal including power down time information and transmits instructions, which is received by each metering unit. Each metering unit extracts the power down time information and transmits instructions from the signal and, if appropriate, transmits data in response to the data transmit instructions; this data being collected by the central data collection unit. The metering units then interrupt the power supply to their transceivers for a period of time which is dependent upon the power down time information. The central data collection unit delays, for a slightly longer period of time before transmitting a further signal via its transceiver, at which time the power supply to the transceiver of each metering unit has already been resumed. By allowing the metering units to power down to a quiescent state under the control of the central data collection unit, flexibility is ensured and power consumption minimized.

This invention relates to telemetry systems of the type which providetwo-way communication between a central data collection unit and one ormore remote data gathering units. Such systems may find application inremote utility metering.

Existing remote metering systems are typically of two types. The firsttype is non-interactive in that the central data collection unit acts asa repository for the data transmitted to it from time to time by theremote data gathering units, but has no control over the timing of thetransmission of such data. Each remote unit may power up, say, onceevery day to transmit its data to the central data collection unit andsubsequently power down to a quiescent state. If the remote units arebattery-powered, this results in battery life being prolonged becausethe remote units are only transmitting for a fraction of their workinglife. However, the inflexibility of one-way transmission and fixedtiming makes it impossible, if the system is used for utilitymonitoring, to monitor peaks and troughs in demand effectively. A systemof this type is disclosed in U.S. Pat. No. 3,924,224 and U.S. Pat. No.4,940,976.

The second existing type of metering system is an interactive system inwhich the central data collection unit polls the remote data gatheringunits from time to time. In this way, the timing of data transmissionfrom the remote units to the central data collection unit is under thecontrol of the central data collection unit's operator or programmer andhence flexible. Nevertheless, there is a drawback and this is that theremote units must at all time be powered up to receive interrogatingsignals from the central data collection unit. Flexibility is gained atthe expense of efficiency of power consumption at the remote units. Ifthe remote units are battery-powered, this will markedly curtail thebattery life. Systems of this type are exemplified by U.S. Pat. No.4,811,011 and GB-2238147-A.

It is an object of the present invention to provide an interactiveremote metering system in which the remote data gathering units arepowered up only when data transmission is required and in which thetiming of data transmission is under the control of the central datacollection unit's operator or programmer. Accordingly, the presentinvention provides a data gathering system comprising one or more remotedata gathering units and a central data collection unit, in which eachremote data gathering unit and the central data collection unit includesa transceiver for the communication of information between the remotedata gathering units and the central data collection unit, the centraldata collection unit comprises means for transmitting via itstransceiver a signal including power down time information, each remotedata gathering unit comprises means for extracting the power down timeinformation from the signal received via its transceiver and means forsubsequently interrupting the power supply to its transceiver for aperiod of time dependent upon the power down time information, and thecentral data collection unit further comprises means for delaying for aperiod of time dependent upon the power down time information beforetransmitting a further signal via its transceiver, at which time thepower supply to the transceiver of each remote data gathering unit hasalready been resumed.

When the central data collection unit is interrogating the remote unitor units, part of the interrogating signal includes information as tothe length of time which will expire before the next interrogatingsignal is transmitted. This may, for example, be four hours, or it maybe ten minutes; it is entirely under the control of the operator orprogrammer of the central data collection unit. Each remote unit, afterreceiving the signal will transmit its data, if instructed to do so, andthen powers down to a quiescent state for the period of time for whichit has been so instructed.

The central data collection unit delays for a similar period of timebefore transmitting its next interrogating signal; but this period oftime will be slightly longer than the period for which the meters arepowered down to a quiescent state to take into account any drift out ofsync which may occur in the meantime between the central data collectionunit and the remote units. As a result, each remote unit will power upbefore the next transmission from the central data collection unit.Where the units keep time by means of internal clock crystals, theperiod of time delayed by the central data collection unit will be agreater number of cycles than that for which the remote units arepowered down to a quiescent state. The difference in number of cycleswill be calculated from the expected maximum drift.

To allow the central data collection unit to extract data from theremote data gathering units, it is preferred that the signal includestransmit instructions, each remote data gathering unit includes meansfor extracting the data transmit instructions from the signal receivedvia its transceiver and means for transmitting data gathered, via itstransceiver, in response to an instruction to do so included in the datatransmit instructions and the central data collection unit includesmeans for extracting from a signal received via its transceiver the dataprovided by one or more remote data gathering units. The central datacollection unit may selectively instruct a sub-set of the remote datagathering units to transmit data with each interrogating signal; theremainder simply power down to a quiescent state for the periodspecified until the next signal.

To ensure that the data transmitted by one remote data gathering unitdoes not interfere with that from others, it is preferred that the meansfor transmitting data gathered includes means for delaying thetransmission of the data gathered for a period of time determined by theunique address attributed to the remote data gathering unit in question.The means for extracting from the signal the data provided by one ormore remote data gathering units may include means for correlating thatdata with individual remote data gathering units in dependence upon thedelay between transmission of the data transmit instructions and receiptof that data. The correlation provides an error checking mechanismbacking up other identification methods, such as transmission by theremote data gathering unit of its unique address.

For security purposes, it is preferred that the signal from the centraldata collection unit include scramble code, each remote data gatheringunit include means for extracting the scramble code from the signalreceived via its transceiver and means for scrambling the data gatheredprior to transmission and the central data collection unit include meansfor unscrambling the signal received via its transceiver using thescramble code. This scramble code may be changed for each transmissionby the central data collection unit.

The data gathering unit and central data collection unit used in themetering system according to the invention possess unique properties.Accordingly, the present invention also provides a data gathering unitcomprising a transceiver for the communication of information betweenthe data gathering unit and a central data collection unit, means forextracting power down time information from a signal received via thetransceiver and means for subsequently interrupting the power supply tothe transceiver for a period of time dependent upon the power down timeinformation.

The data gathering unit may comprise a meter adapted to measure apredetermined quantity, e.g. a utility meter. The data gathering unitmay be battery-powered and its transceiver may be adapted to communicateby radio.

As explained above, the data gathering unit preferably includes meansfor extracting data transmit instructions from the signal received viaits transceiver and means for transmitting data gathered, via itstransceiver, in response to an instruction to do so included in the datatransmit instructions.

The means for transmitting data gathered may include means for delayingthe transmission of the data gathered for a predetermined period oftime.

The present invention further provides a central data collection unitcomprising a transceiver for the communication of information betweenthe central data collection unit and one or more remote data gatheringunits, means for transmitting via the transceiver a signal includingpower down time information and means for delaying for a period of timedependent upon the power down time information before transmitting afurther signal via its transceiver.

The transceiver may be adapted to communicate by radio.

Again, the signal preferably includes transmit instructions and thecentral data collection unit includes means for extracting from a signalreceived via its transceiver data provided by one or more remote datagathering units in response to an instruction to do so included in thedata transmit instructions.

The means for extracting from the signal data provided by one or moreremote data gathering units may include means for correlating that datawith individual remote data gathering units in dependence upon the delaybetween transmission of the data transmit instructions and receipt ofthat data.

The present invention also extends to a method of collecting data fromone or more remote data gathering units each including a transceiver forthe communication of information, means for extracting power down timeinformation from a signal received via its transceiver and means forsubsequently interrupting the power supply to its transceiver for aperiod of time dependent upon the power down time information, themethod comprising transmitting a signal to each remote data gatheringunit including power down time information to be extracted and delayingfor a period of time dependent upon the power down time informationbefore transmitting a further signal to the remote data gathering units,at which time the power supply to the transceiver of each remote datagathering unit has already been resumed.

Preferably, the signal includes transmit instructions, each remote datagathering unit includes means for extracting the data transmitinstructions from the signal received via its transceiver and means fortransmitting data gathered, via its transceiver, in response to aninstruction to do so included in the data transmit instructions and themethod further includes extracting from a signal transmitted by one ormore remote data gathering units the data provided by one or more ofthem.

The means for transmitting data gathered may include means for delayingthe transmission of the data gathered for a predetermined period of timeunique to the remote data gathering unit in question. The method mayinclude correlating the data provided by one or more remote datagathering units with individual remote data gathering units independence upon the delay between transmission of the data transmitinstructions and receipt of the data.

The present invention will now be described with reference to theaccompanying schematic drawings of a remote utility metering system.

FIG. 1 is a system block diagram.

FIG. 2 is a diagram of the functional blocks of the transceiversembodied in the remote data gathering units.

FIG. 3 is a diagram of the system transmission protocol.

As can be seen from FIG. 1, the system includes a central datacollection unit 10, 20 and one of more remote data gathering units,which in this application are metering units 12. The metering unit 12may be an electricity meter, gas meter, water meter, etc. and isinstalled within the locality of a subscriber's premises. The meteringunit 12 and the central data collection unit 10, 20 communicate with oneanother by radio and RF antennae 14, 16 are provided for this purpose.

The central data collection unit 10, 20 illustrated has a group datacollection unit 10 installed on a lamp standard 18 which communicates,via a modem and the public telephone network, with a computer controlstation 20. The group data collection unit 10 is preferably mounted inan elevated position and is able to communicate with a radial group ofmetering units 12. In practice, more than one group data collection unit10 will be provided for each computer control station. The computercontrol station 20 implements billing and tariff control on the basis ofinformation received from the group data collection unit 10. Themetering unit 12 is battery-powered and includes a low-power transceivermodule with integral antenna 16.

Data is transferred from the utility meter through an appropriate knowninterface to the transceiver of the metering unit 12 for transmission.The system is controlled by the central data collection unit 10, 20 viathe radio links to the metering units 12. For this purpose, a uniquecommunications protocol has been developed and will be discussed belowwith reference to FIG. 3.

FIG. 2 illustrates the functional blocks of the metering units 12 andthe group data collection units 10. Each such unit 10, 12 includes anantenna 104, 104', a transmitter 100, 100', a receiver 102, 102' and aswitch 106, 106' which selectively connects the receiver 102, 102' orthe transmitter 100, 100' to the antenna 104, 104'. The switch 106,106', transmitter 100, 100' and receiver 102, 102' are controlled by aCPU or other control circuit 108, 108', which selects either thetransmitter 100, 100' or the receiver 102, 102' and also outputs thetransmission bitstream to the transmitter 100, 100' or extracts areceived bitstream from the receiver 102, 102'. Any form of transmitter100, 100', receiver 102, 102' and switch 106, 106' would be appropriateto the present invention so long as the control circuits 108, 108' caneffectively communicate with one another.

Apart from the transceiver functions, the remaining functions of themetering unit 12, viz. data processing, security coding--if desired,address decoding and transceiver power control may be performed by asecond circuit, for example a low-power CMOS IC which may be a suitablyprogrammed CPU. This CPU may be the same as or different from thecontrol circuits 108, 108', already mentioned. The CMOS IC may use a lowfrequency crystal as its clock. With the metering unit's transceiverpowered up for the time being, signals received via the transceiver aremonitored by the CMOS IC.

As soon as an incoming signal is recognized as originating with thecentral data collection unit 10, 20, the CMOS IC separates it into powerdown time information and transmit instructions. If the transmitinstructions apply to the particular metering unit 12 in question, ittransmits its data in a predetermined form to the central datacollection unit 10, 20 and then the transceiver is powered down to aquiescent state; if the transmit instructions do not apply to theparticular metering unit 12, the receiver is immediately powered down toa quiescent state.

Each metering unit 12 has a unique programmed address, and interferencebetween the transmissions from various metering units 12 is prevented bya transmission delay feature. The CMOS IC of each metering unit delaystransmission of the metering unit's data by a period of time which isdifferent for each metering unit and is linked to the metering unit'sunique address.

As will be explained below, the metering units identify themselves tothe central data collection unit by transmitting back their uniqueaddresses. The central data collection unit 10, 20, as an additionalcheck, correlates the data received in reply to its signals according totime elapsed between the transmission of its signal and the receipt ofdata in reply with individual metering units 12. This is done either bymeans of correlation look-up tables or by calculations based on aone-to-one mapping between metering unit address and delay time.

The transceiver of each metering unit 12 is powered down to a quiescentstate for a time dependent upon the power down time informationcontained within the signal from the central data collection unit 10. Inone system, as described below, the power down time information may be aseven bit number representing power down time in units of five minutes.This allows power down times of between five minutes and ten hours fortyminutes.

Similarly, once all data is received, the central data collection unit10, 20 waits for a period of time slightly longer than the power downtime of the metering units, to ensure that these units are all poweredup to receive notwithstanding any clock drift in the meantime, and thentransmits its next signal. This signal then triggers the re-setting ofthe metering units' power down time counters such that they all begincounting the next period at the same instant.

As a safeguard on battery power, the metering units 12 may only power upfor a relatively short period of time, such as 10 ms for example. Thisensures that should the metering unit 12 and the central data collectionunit 10, 20 become out of step with one another, for example owing totransmission artifacts, the metering unit will power down to a quiescentstate after its 10 ms waiting period. As a result, a limitation isplaced on the amount of time between signals from the central datacollection unit 10, 20, to ensure that the various metering units andthe central data collection unit do not drift out of sync by more than10 ms, for example.

To enable the metering unit to get back on stream without having to bereset by a remote operative, it will transmit at half the last timedelay plus its own unique address-related delay to alert the centraldata collection unit 10, 20 and repeatedly power up at fixed knownintervals, e.g. 5 mins, to enable reactivation by the central datacollection unit 10, 20, increasing the period for which it powers up itsreceiver by, say, 20 ms at each of these intervals until a limit, e.g.200 ms, is reached, at which point it powers down until manuallyserviced.

When not transmitting, the central data collection unit 10, 20 listensfor metering units 12 and, following receipt of an unsolicitedtransmission from a metering unit 12 will transmit at intervals of, say,5 mins for 10 times to the metering unit in question with power downtime information which will bring it into synchrony with any otherswhich the central data collection unit communicates intentionally. Themetering unit 12, upon receipt of the timing correction signal from thecentral data collection unit, will transmit an acknowledgement signal tothe central data collection unit 10, 20 whereupon the latter will ceaseto transmit the timing correction signals.

FIG. 3 illustrates the communications protocol which has been developedto deliver the functionality discussed. For communication from themetering units 12 to the central data collection unit, an eight bitserial protocol 30 is proposed having eight data bits 60, combined withstart 62, stop 64 and parity bits 66 and scrambling. For communicationfrom the central data collection unit 10, 20 to the metering units 12,the transmit protocol 32 is a string of eight bit words 68 with apreamble, but no start, stop or parity bits. This allows the meteringunit control circuit 108 to be simplified.

The central data collection unit protocol 34 commences with an eight bitpreamble 40 which enables the metering units 12 to detect the start of anew message. The next twenty-four bits 54 are dedicated to metering unitaddressing. The first eight bits 42 are for group addressing, giving amaximum of 256 groups within radio range of the group data collectionunit or units 10. The group address bits 42 enable the metering units 12to determine that the signal received is sent by the central datacollection unit 10. The next four bits 44 are control bits to indicatewhether group, sub-group or individual metering unit addressing is beingused. The final twelve bits 46 are the metering unit address, giving amaximum of 4096 metering units per group.

If individual metering unit addressing is specified, only one meteringunit 12 will transmit data in reply and the transmission delay need notbe applied. However with group or sub-group addressing, where more thanone metering unit 12 will transmit in reply, the unique delay will comeinto play for each metering unit. The unique delay for each meteringunit 12 addressing may differ in the case of group addressing from whatis it for sub-group addressing, to ensure that all metering units 12will transmit their data in as short a time as possible.

The next eight bits in the transmission protocol are used to control themetering unit receiver. The first seven 48 represent the power downperiod in units of 5 minutes. The final bit 50 of these eight indicateswhether the metering units 12 are to transmit data; or whether thesignal is purely for re-synchronization purposes.

The final sixteen bits 52 are pseudo-random code which are used fordynamically controlled scrambling of the metering unit's transmission.These bits are stored by the central data collection unit 10, 20 and maybe used to descramble the incoming data from the metering units 12.

The metering unit transmission protocol 34 consists of three bytes 56which are the group and metering unit address combined with the fouraddressing control bits as transmitted from the central data collectionunit. There then follow n bytes of meter data 58--in this case n being4--and these data are used for tariff control and billing by the centraldata collection unit 10, 20. All n+3 bytes are scrambled prior totransmission, e.g. by modulo-2 addition of the sixteen bit pseudo-randomnumber applied to each pair of bytes. If n is even, the odd byte leftwill be scrambled by utilizing the first eight bits of the pseudo-randomnumber.

I claim:
 1. A data gathering unit comprising a transceiver for thecommunication of information between the data gathering unit and acentral data collection unit, means for transmitting data in response toa signal received via the transceiver, means for extracting power downtime information from the signal received via the transceiver and meansfor subsequently interrupting the power supply to the transceiver for aperiod of time dependent upon the power down time information.
 2. A datagathering unit according to claim 1 in which the data gathering unitcomprises a meter adapted to measure a predetermined quantity.
 3. A datagathering unit according to claim 2 in which the meter is a utilitymeter.
 4. A data gathering unit according to claim 1 which isbattery-powered.
 5. A data gathering unit according to claim 1 in whichthe transceiver is adapted to communicate by radio.
 6. A data gatheringunit according to claim 1 including means for extracting data transmitinstructions from the signal received via its transceiver and means fortransmitting data gathered, via its transceiver, in response to aninstruction to do so included in the data transmit instructions.
 7. Adata gathering unit according to claim 6 in which the means fortransmitting data gathered includes means for delaying the transmissionof the data gathered for a predetermined period of time.
 8. A datacollection unit comprising a transceiver for the communication ofinformation between the data collection unit and one or more remote datagathering units, means for transmitting via the transceiver a signalincluding power down time information and means for delaying for aperiod of time dependent upon the power down time information beforetransmitting a further signal via its transceiver.
 9. A data collectionunit according to claim 8 in which the transceiver is adapted tocommunicate by radio.
 10. A data collection unit according to claim 8 inwhich the signal includes transmit instructions and the data collectionunit includes means for extracting from a signal received via itstransceiver data provided by one or more remote data gathering units inresponse to an instruction to do so included in the data transmitinstructions.
 11. A data collection unit according to claim 10 in whichthe means for extracting from the signal data provided by one or moreremote data gathering units includes means for correlating that datawith individual remote data gathering units in dependence upon the delaybetween transmission of the data transmit instructions and receipt ofthat data.
 12. A telemetry system comprising one or more remote datagathering units and a central data collection unit, in which each remotedata gathering unit and the central data collection unit includes atransceiver for the communication of information between the remote datagathering units and the central data collection unit, the central datacollection unit comprises means for transmitting via its transceiver asignal including power down time information, each remote data gatheringunit comprises means for extracting the power down time information fromthe signal received via its transceiver and means for subsequentlyinterrupting the power supply to its transceiver for a period of timedependent upon the power down time information, and the central datacollection unit further comprises means for delaying for a period oftime dependent upon the power down time information before transmittinga further signal via its transceiver, at which time the power supply tothe transceiver of each remote data gathering unit has already beenresumed.
 13. A telemetry system according to claim 12 in which thesignal includes transmit instructions, each remote data gathering unitincludes means for extracting the data transmit instructions from thesignal received via its transceiver and means for transmitting datagathered, via its transceiver, in response to an instruction to do soincluded in the data transmit instructions and the central datacollection unit includes means for extracting from a signal received viaits transceiver the data provided by one or more remote data gatheringunits.
 14. A telemetry system according to claim 13 in which the meansfor transmitting data gathered includes means for delaying thetransmission of the data gathered for a predetermined period of timeunique to the remote data gathering unit in question.
 15. A telemetrysystem according to claim 14 in which the means for extracting from thesignal the data provided by one or more remote data gathering unitsincludes means for correlating that data with individual remote datagathering units in dependence upon the delay between transmission of thedata transmit instructions and receipt of that data.
 16. A telemetrysystem according to claim 13 in which the signal includes scramble code,each remote data gathering unit includes means for extracting thescramble code from the signal received via its transceiver and means forscrambling the data gathered prior to transmission and the central datacollection unit includes means for unscrambling the signal received viaits transceiver using the scramble code.
 17. A method of collecting datafrom one or more remote data gathering units each including atransceiver for the communication of information, means for extractingpower down time information from a signal received via its transceiverand means for subsequently interrupting the power supply to itstransceiver for a period of time dependent upon the power down timeinformation, the method comprising transmitting a signal to each remotedata gathering unit including power down time information to beextracted and delaying for a period of time dependent upon the powerdown time information before transmitting a further signal to the remotedata gathering units, at which time the power supply to the transceiverof each remote data gathering unit has already been resumed.
 18. Amethod according to claim 17 in which the remote data gathering unitscomprise meters adapted to measure a predetermined quantity.
 19. Amethod according to claim 18 in which the meters are utility meters. 20.A method according to claim 17 in which the remote data gathering unitsare battery-powered.
 21. A method according to claim 17 in which thetransceivers are adapted to communicate with one another by radio.
 22. Amethod according to claim 17 in which the signal includes transmitinstructions, each remote data gathering unit includes means forextracting the data transmit instructions from the signal received viaits transceiver and means for transmitting data gathered, via itstransceiver, in response to an instruction to do so included in the datatransmit instructions and the method further includes extracting from asignal transmitted by one or more remote data gathering units the dataprovided by one or more of them.
 23. A method according to claim 22 inwhich the means for transmitting data gathered includes means fordelaying the transmission of the data gathered for a predeterminedperiod of time unique to the remote data gathering unit in question. 24.A method according to claim 23, further including correlating the dataprovided by one or more remote data gathering units with individualremote data gathering units in dependence upon the delay betweentransmission of the data transmit instructions and receipt of the data.25. A method according to claim 22 in which the signal includes scramblecode, each remote data gathering unit includes means for extracting thescramble code from the signal received via its transceiver and means forscrambling the data gathered prior to transmission and the methodincludes unscrambling the signal received via its transceiver using thescramble code.